1. Scope of the Invention
This invention relates to a wideband 180xc2x0 microwave phase switch structure, its object being the configuration of a 180xc2x0 switch with optimally balanced phase and amplitude along a high band width with low-loss along all the band, of particular interest in high frequency and low cost applications, as well as in high power applications.
2. Background of the Invention
The interest in 180xc2x0 phase switch structures in the area of microwave and millimetric waves has increased due to their possible use in communications and stabilisation circuits for scientific measuring among others. With the great increase experienced by digital communications the employment of using only the amplitude switch has passed on to its being used jointly with the phase switch. The latest technological advances have also incorporated the phase switch as stabilisation means of certain types of radiometers.
The phase switch can be performed by means of two DPST (Double-pole-single-throw) switches, FET type (Field Effect Transistor), HEMT (High Electron Mobility Transistor) or PIN diode at each end of two different lengths of a transmission line, in such a way, that it is possible to switch from one to the other. The difference between the switching from one to the other of these line lengths for a given frequency, produces a 180xc2x0 phase difference in the output signal. This is a very narrow band technique (10% ). A wider band can be obtained if the transmission lines are replaced by circuits with appropriate characteristics.
A more compact design that increases the band width is achieved by means of a Lange type 90xc2x0 coupler. PIN, HEMT or FET diode switches are placed between the two output ports of the coupler and mass causing an open circuit or short-circuit in both. The resulting reflection through the isolated coupler port can phase-switch by 180xc2x0 depending on the condition of the switches. This phase switch is of relatively wide band with compact construction, however, it is more prone to unbalance between the two conditions due to the characteristics of the switches. There are more recent designs that use this method with a Balun coupler instead of the Lange coupler (Microwave Journal, December 1999). The resulting configuration is more compact. A design has recently appeared with 4 Baluns and one DPDT (double-pole-double-throw) switch with a very wide band (120% )
Much attention has been paid to the Magic-T or Rat-Race hybrid ring circuit (which is also a 180xc2x0 coupler) throughout the past 20 years. The ring has been optimised with the purpose of obtaining a high bandwidth ( greater than 40%). Various designs have arisen by means of which the band width is raised, using non flat technology instead of the middle wave length line (asymmetric part) of the ring. The resulting ring is more symmetrical and the bandwidth is only limited by the interconnection of the quarter length wave sections. The hybrid ring can be described as a divider or 180xc2x0 coupler, and is particularly useful in mixer and coupling signal circuits.
Other phase switches use active circuit properties such as FET to obtain phase increases. There are designs by means of which, what is obtained is a continuous phase variation between 0 and 360xc2x0. More recently interest has focused on wideband 180xc2x0 phase switches, flat phase and balanced amplitude in aerospace scientific missions. In order to detect backwall cosmic radiation fluctuations in the microwave margin, radiometers with cryogenic refrigeration have been used, based on HEMT technology. Missions, as for example, MAP (Mocrowave Anisotropy Probe) and the Plank Surveyor, have used the wideband 180xc2x0 phase switch to stabilise their radiometers. Balanced amplitude and phase are essential for design in order to reduce l/f noise introduced by the HEMT amplifiers. Various thousands of stabilisation factors have been achieved (Meinhold and others, 1999).
The wideband 180xc2x0 microwave phase switch, is constituted by any microwave or millimetric guide, such as waveguides, microstrips, strip-lines, coaxial cables etc., with a set phase length.
The design is based on the interconnection of two hybrid rings (magic T) that are embodied according to a given configuration of the different ports of the two rings, thereby providing a unique structure resulting in a practical application device with a 180xc2x0 phase difference characteristic and given properties relative to the length of the waves and the impedances relative to the resulting lines.
Specifically, the 180xc2x0 phase switch incorporates a microwave or millimetric wave symmetrical circuit with two possible input ports and another two output ports, in such a way that only an input and an output port are simultaneously connected. Both the two input ports and the two output ports are connected by means of a transmission or waveguide line that is equivalent to half the central frequency wavelength of the specific band. Each transmission waveguide line has characteristic root of two impedance, multiplied by the characteristic impedance of the system it belongs to.
Each input port is connected to a different output port by means of a transmission or waveguide line that is equivalent to half the wave length of the specific central band frequency. Each transmission or waveguide line has a characteristic root of two impedance multiplied by the characteristic impedance of the system it belongs to.
The central points of the transmission or waveguide lines between the input and the output ports are interconnected by means of a transmission or waveguide line that is equivalent to half the wave length of the relative central band frequency. Each transmission or waveguide line has a characteristic impedance of the system it belongs to, divided by the root of two.
It relates to a wideband and balanced amplitude and phase structure that can be used as 180xc2x0 difference phase switch or passive structure. It is appropriate for almost all types of transmission line designs. It can be incorporated in a waveguide using the characteristic guide wave lengths and the actual characteristic impedances of the structure.